In-mold labeling (IML) is the use of paper or plastic labels during the manufacturing of containers or other articles by blow molding, injection molding, or thermoforming processes. The label or insert serves as the integral part of the final product, which is then delivered as pre-decorated item.
IML is primarily used today for decorating injection molded parts for consumer electronics and for plastic cups and bottles. Manufacturers are adopting IML technology for greater wear resistance than traditional printing of molded articles, and for better adhesion to the underlying molded article or container. This is because a film, such as a transparent polymeric film, is printed on one side with decorative ink. The printed film is converted into a label, which is then positioned on a mold wall of an injection molding die or tool. Injection plastic, in the form of a heated or molten plastic shot, is introduced into the mold in contact with one side of the film, either the ink side (with protective layers therebetween) or the non-ink side. When the plastic shot material is introduced such that it is proximate the ink side of the label, this fuses to a non-printed surface of the label, and encapsulates the decoration between the film layer of the label and the injected plastic resulting in a decoration that cannot be abraded during use.
Further, IML can provide greater decorating options than other methods. For example, multi-color offset lithography printed graphics or digital graphics are used to produce products with higher quality graphics than available with other decorating methods.
During the molding process, robotics can be used to sense and position a label in the mold tool, such as a steel mold. Vacuum and compressed air can be used to hold the label in place during the molding process. Alternatively, static electricity can be used. In the case of static, electrostatic charging electrodes shot a label while it is being transferred to the molding machine, so that when the label is placed on the tool and released by the labeling robot, it will wrap itself onto or into the tool, and remain on the tool until the article is molded and cooled.
The in-mold labels can be formed from paper or a similar material to the plastic shot material. For example, polypropylene or polystyrene is commonly used as label material, with a thickness of ranging from about 15 to 100 micrometers; however the thickness of the label can be thinner or thicker than the exemplary, non-limiting range, depending on the final application or desired molded product. For example, for handling and structural integrity of a molded container, a label thickness in excess of 100 micrometers may be desired. For applications for molded products that are instead lightweight, have complex shapes such that conformity to shape is desired, do not require excessive structural integrity, and/or for the purpose of keeping manufacturing and shipping costs down, labels less than 15 micrometers in thickness can be contemplated.
Cavitated materials can also be used. Cavitated materials are sandwich or layered materials, having a spongy layer bonded between two or more very thin solid, or functional layers. An advantage of cavitated film is better conformance to small-radius curves on a product. Laminated films can also be used, with or without cavitated materials, to decorate products, yielding high wear-resistance. This type of film can have the printed surface protected by a second layer of film, such that the label has a total thickness of about 15 or 40 micrometers; however, as described above the thickness of the label can be thinner or thicker than the exemplary, non-limiting range, depending on the final application or desired molded product.
The standard films used in in-mold labeling are inherently good or excellent water vapor barriers. However, they are not oxygen barriers, which can be desired for packaging of certain consumable products. The following table is an example of typical oxygen, carbon dioxide, and moisture or water vapor transition rates of common types of films used in packaging, wherein MVTR stands for Moisture Vapor Transmission Rate in g-mil/100 in.2/24 hr, and O2 and CO2 stand for Oxygen Transmission Rate (OTR) and Carbon Dioxide Transmission Rate (COTR), respectively, in cm3-mil/m2/24 hr.
MaterialMVTRO2TRCO2TRPET (Oriented or Stretch2.075540Blown PolyethyleneTerephthalate)HDPE (High Density0.54,00018,000Polyethylene)PVC (Polyvinyl Chloride)3.0150380PP (Polypropylene)0.53,5007,000PS (Polystyrene)10.06,00018,700PLA (Polylactide -18-2238-42201Oriented/Stretch Blownbottles)
One non-limiting example of desired barrier properties for packaging of consumable products include a Water Vapor Transmission Rate (WVTR) of 0.010 g/100 in2/day at 84.4° F./80% RH and an Oxygen Transmission Rate (O2TR) of 0.0041 cc/100 in2/day at 73° F./0% RH. Other barrier properties, in addition to or alternatively to water vapor and oxygen, can also be desired depending on the product being molded and its final use or application. Such properties can include, but are not limited to, light (e.g. UV), aroma, and/or flavor retention. The desired barrier properties of the final molded product are application specific and depends on, for example, the product being contained within the molded article, the perceived shelf life of the product, the sensitivity of the product to environmental factors, and/or the different spoilage or failure mechanisms that define when the product has “expired” or “gone bad.” Because existing in-mold technologies do not offer many of the desired barrier properties for consumable product, applications of the existing in-mold technologies is therefore limited to containers such as cups or other decorative articles, and are not used for packaging consumable products or products with a shelf life, including, but not limited to, liquid and solid foods, medications, toiletries such as perfumes and toothpaste, beverages, paints, adhesives, or the like.
Films with both water vapor and oxygen barrier properties are commonly used in the pouching industry for packaging of foods such as fatty foods, sauces and liquids, medical devices or instruments, medicines, and the like. These films are typically multi-layer or composite films that include a barrier film and are specifically constructed based on the intended use of the pouch. These barrier films can include, for example, coextruded, peelable heat-seal films and silicon oxide/aluminum oxide composites, or metallic films or films having a vacuum-deposited layer of metallic material such as aluminum oxide (Al2O3) or silicon oxide (SiOx). Some of these can withstand retort or other sterilization (e.g. autoclave) processes that can reach temperatures in excess of 270 degrees Fahrenheit for extended periods of time (e.g. 70 minutes or more) depending on the contents of the pouch and the sterilization needs.
The films used in the pouching industry, however, do not necessarily translate into the in-mold labeling industry. To create an adequate seal, an in-mold label is preferably overlapped and sealed onto itself in the molding process to ensure a complete seal. However, these thin solid films cannot seal to themselves in injection-molded processes. These film are also oftentimes too thin to be efficiently use in injection molding processes because they are difficult to place and maintain within a mold. Furthermore, these films are sometimes not compatible with the plastic shot materials of the molding process such that the label does not adhere well to the underlying molded article and can peel away from the article, therefore breaching the seal or barrier.
In-mold labels having barrier properties have been recently developed. One example of an in-mold label having barrier properties is a composite film that includes a layer of ethyl vinyl alcohol encapsulated or sandwiched between two polymeric layers, such as cast polypropylene, that readily adheres to the underlying shot material to such that the label does not peel away. However, these labels are expensive due to the amount of material needed to create adequate barrier properties. Furthermore, downgauging of these materials is difficult for applications in which conformity to a complex shape is desired. Downgauging refers to reducing the amount of material in a product while still maintaining or even improving the properties of that material. When these films are downgauged, the barrier properties are often compromised and/or eliminated.
These labels also are not able to seal upon themselves such that an overlap cannot be created. Rather, a precise butt splice must be created such that the label meets exactly end to end without breach of the barrier. This requires expensive precision cutting equipment, robotic placement systems, and can generate large volumes of waste if the label is neither cut precisely nor placed correctly into the mold.
Finally, these films, although adequate for dry barrier applications such as dry foods, cannot withstand retort or sterilization processes as described above, or other processes performed at high temperatures and/or pressures for extended periods of time, thereby compromising the barrier properties of the film.
There remains a need for a film for use in in-mold labeling technologies that offers adequate barrier properties, such as water vapor and oxygen barriers, and that can withstand molding processes, retort or other sterilization or pasteurization processes, and other such intense processes without compromising the barrier properties. Preferably, the film is similarly in cost to standard in-mold labels.